I don't know about others, but I have had no issues with a 944 upgrade and 41 flats w/ long manifolds. I first did the 944 kit, then I did the carbs. I have never had an issue with it, probably because I had a great mechanic do everything for me. There is a downside with higher compression...your starter will go bad alot quicker (pre-98). I already had to clean up my starter and redue the brushes. though going to a higher guage wire to the starter has helped. Also, compression ratios for pistons...ie 12:1, 12.5:1, 13:1 etc.... You NEVER get the actuall compression. You get a 1 to 0.5 less then that actually stated for the pistons. IMHO, if you have the money, go with the big bore kit and then later do the carbs.